In integrated circuit design, it is often desirable to have the ability to programmably create a connection between two nodes. A device which performs this function is referred to as an "antifuse". An antifuse differs from a fuse in that the initial condition of the antifuse is an open circuit, which is closed upon application of a sufficient voltage between the leads of the antifuse. A fuse, on the other hand, is initially a short-circuit, which becomes an open circuit upon applying a sufficient voltage to the leads of the fuse.
One important application for antifuses is high density programmable gate array logic where devices are programmably connected to implement a desired function. Programmable gate array logic differs from normal gate array logic in that the customer may perform the programming rather than the vendor.
Several devices have been used or proposed to supply the programmable element of a programmable gate array. SRAM and EPROM cells provide proven technology, but require a large device area, thereby limiting the number of programmable elements on the gate array. A polysilicon-to-diffusion oxide antifuse (which has polysilicon and doped silicon leads separated by an oxide barrier) has higher integration possibilities, but its performance is limited due to high junction capacitance of the diffused area. Further, the capacitance increases proportionately to the number of connected antifuses.
A polysilicon-to-polysilicon amorphous silicon antifuse (which has polysilicon leads and an amorphous silicon barrier) has potentially high integration, but suffers from high leakage and limited performance due to high polysilicon resistance. Further, the manufacturing costs of this process and the complexity of the process substantially increase the cost of providing the antifuses.
A polysilicon-to-polysilicon oxide antifuse also has potentially very high integration, but suffers from limited performance due to the high polysilicon resistance and the added manufacturing costs and complexity.
Metal-to-metal antifuses have been proposed using a deposited oxide and/or nitride layer between the metal layers. While this concept has the advantages of very high integration and high performance, a significant problem is the integrity of the antifuses due to the process control on the deposited dielectric film layer. The deposited oxide and/or nitride layer must be relatively thin in order to form a connection between the two metal layers responsive to a voltage in the range of 8-18 volts. For not being an integral part of the underlying metal layer, this thin dielectric film is deemed to suffer unwanted short-circuits between the two metal layers during the subsequent metal sintering process at 450.degree. C.
An antifuse formed by growing an oxide region on an underlying layer of aluminum or aluminum compound metal is disclosed in U.S. patent application Ser. No. 07/626,810 for an Antifuse and Method of Forming the Same, which application is hereby incorporated by reference. However, aluminum is not a refractory metal. Therefore this antifuse cannot withstand temperatures in excess of approximately 400.degree. F. This temperature limitation can be disadvantageous in the event that the integrated circuit in which the antifuse is formed must be subjected to temperatures higher than 400.degree. F. in subsequent manufacturing processes.
Therefore, a need has arisen in the semiconductor fabrication industry to provide a metal-to-metal antifuse with high processing integrity, and which can also withstand high processing temperatures.